<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>被选元素的结尾插入内容</title>
		<script src="js/jquery-3.3.1.min.js" type="text/javascript" charset="utf-8"></script>
	</head>
	<body>
		<ol class="o1">
			<li>高等数学</li>
			<li>线性代数</li>
			<li>概率统计</li>
		</ol>
		<button type="button" class="bu1">结尾追加</button>
	</body>
</html>
<script type="text/javascript">
	$(document).ready(() => {
		$("button:eq(0)").click(() => {
			$("body>.o1").append("<li>大学英语</li>");
		})
	})
</script>